Toughening and strengthening of advanced ceramics with rare earth additives
Introduction
At present, Al2O3-based ceramic material is one of the most widely used ceramics in practice. However, the intrinsic brittleness still exists as a fatal weakness for ceramic materials. In order to reduce the brittleness and to increase the strength and toughness, a great deal of research work has been done [1], [2], [3]. Mechanical properties of alumina-based ceramics have been improved by the incorporation of one or more reinforcing phases such as TiC, TiN, TiB2, SiC particulates, SiC whiskers, B4C, ZrO2, WC, (W,Ti)C, Ti(C,N), Cr3C2, NbC, etc. Investigations on toughening mechanisms such as crack deflection, crack branching, crack bridging, microcracking, transformation, toughening by residual thermal stress and their synergistic interactions, etc. are still active [1], [4], [5], [6], [7], [8].
Rare earth elements, working as a series of effective additives, have got widespread applications in current research of advanced ceramic materials [9], [10]. They can be used not only as the stabilizer of the tetragonal zirconium oxide but as the sintering aid for Al2O3, TiB2, TiC, SiC, Si3N4, sialon and AlN ceramics [9], [10], [11], [12]. As a result, physical and mechanical properties of these ceramics have been noticeably enhanced. However, other possible acting mechanisms of rare earth elements have rarely been reported elsewhere. In the present study, Al2O3/(W,Ti)C ceramic composites reinforced by rare earth additives are fabricated. Microstructure, mechanical property, toughening and strengthening mechanisms and cutting performance are investigated in detail.
Section snippets
Experimental procedures
Commercially available high purity alumina and (W,Ti)C powders were used as the starting materials with average sizes of 0.8 μm and 1.0 μm, respectively. The raw materials were blended with each other (with 35 wt.% (W,Ti)C) and doped with different amounts up to 2 wt.% of pure rare earth metal additive such as yttrium (Y). The doping process and the following ball-milling process have been performed under a N2 protective atmosphere. The mixtures were subsequently homogenized with absolute alcohol
Mechanical property
The maximum flexural strength of Al2O3/(W,Ti)C ceramics is about 853 MPa when 0.25 wt.% Y is added (Fig. 1), which is about 20% higher than that of the corresponding material without yttrium. Then, with the increase of yttrium content, the flexural strength decreases slowly.
Under the experimental conditions, the incorporation of yttrium can improve the fracture toughness of Al2O3/(W,Ti)C ceramic materials when its content is less than 1.5 wt.% (Fig. 2). Particularly, when 0.5 wt.% Y is added the
Conclusions
The addition of rare earth additives such as yttrium of a suitable amount in a proper way can notably improve the flexural strength and fracture toughness and fracture resistance of Al2O3/(W,Ti)C ceramic material.
Acknowledgements
The Foundation for University Key Teacher by the Ministry of Education, China (Grant No. 2058), the Research Fund for the Excellent Young & Middle-aged Scientists, Shandong Province (Grant No. 2000-49) and the Natural Science Fund, Shandong Province (Grant No. Y2001F02), are all greatly appreciated for supporting this project.
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